All-Electric Subsea Well Brings Benefits vs. Traditional Hydraulic Technology

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27701, “World-First All-Electric Subsea Well,” by Thomas Schwerdtfeger, Total E&P Netherlands; Bruce Scott, Halliburton; and Jan van den Akker, SPE, OneSubsea, a Schlumberger Company, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. Currently, the state of the art for subsea well control is based on hydraulic technology. Hydraulic fluid is supplied from a host facility to the subsea wells through dedicated tubes within an umbilical and is distributed to the wells. Shifting that trend, K5F3, the world’s first all-electric well in the subsea industry, opened to production on 4 August 2016. This paper presents the benefits of electric subsea control compared with current state-of-the-art hydraulic methods. Rationale for Electric Production System Expenditure Savings. When looking at the introduction of a new technology such as an electric system, successful introduction is a direct consequence of a perceived reduction in capital expenditure (CAPEX) and factors such as operating expenditure (OPEX); health, safety, and environment (HSE); and future readiness also need to be addressed. To perform preliminary system engineering for the implementation of the electric system and provide a comparison with a conventional electrohydraulic multiplex system, a case with five oil-production wells, one gas-injection well, and three water-injection wells was used as a base case for cost. The study concludes that the electric system is likely to show a range of benefits over the equivalent electrohydraulic multiplex system. Improved System Efficiency. Electric subsea production brings advantages in most scenarios, particularly in an ultradeepwater field or with long-distance step outs. Electric motors maintain their high level of efficiency and full torque capability regardless of water depth, unlike hydraulic pressure, which must over-come seawater hydrostatic pressure. Use of high-voltage direct current for long-distance power transmission is far more efficient than use of either alternating current or hydraulic pressure. Removing hydraulic tubing from the umbilical and reducing the number of conductors bring several advantages. The electric umbilical has a smaller cross section, allowing longer continuous lengths to be manufactured and spooled. Overall weight is reduced, facilitating the use of a smaller installation vessel. And, on very long stepouts, splices in the umbilical can be either reduced or eliminated altogether. HSE Improvement. An all-electric system eliminates the discharge of hydraulic fluid to the environment and hydraulic-pressure safety issues. Future Potential and Readiness. Having much higher levels of electric power available at the subsea end of the system (compared with the electrohydraulic system) offers a greater scope for powering additional tools and sensors such as multiphase flowmeters. It also facilitates the addition of intelligent wells, new sensors, and digital flow-control valves.